WebTP: Protocol Design Issues Jeng Lung & Yogesh Bhumralkar

Introduction Following key issues related to the design and testing of the protocol: –Congestion Window Control –Retransmission Timeout Scheme –Performance under Network Jitter

Congestion Control Background –WebTP uses TCP-style congestion control –2 Phases: Slow Start Congestion Avoidance: Additive Increase/Multiplicative Decrease –TCP biased against long connections; therefore, WebTP faces same dilemma.

Improving Fairness Maximize fairness by modifying Additive Increase Instead of increasing cwnd by 1/cwnd, increase it by K=c*rtt*rtt. This makes it more fair Problem: Find optimal K for fairness K is topology dependent but still want to ensure that the scheme works for WebTP.

Network Topology

Retransmission Scheme Current timeout set to: M is the receiver’s tolerance to jitter. Examine the effects of changing M on the number of dropped and duplicate packets.

Jitter Study Any network has considerable random delays. The time between when the packet is transmitted to when it reaches the receiver varies a great deal - this phenomenon is called jitter. Simulated jitter by introducing random delay to each packet on the sender side.

Conclusion Congestion Window Scheme: Optimal K depends on network topology. Retransmission Scheme: Dropped packets increase with M whereas the number of duplicate packets goes down at higher M. Network Jitter: Higher jitter implies that a higher M is required to handle the delays that are introduced.